1. Field of the Invention
This invention relates to a scroll fluid machine used for compressors, such as air compressors and refrigerant compressors, pumps, expanders or the like, in particular to a gap-fine regulation mechanism of a scroll fluid machine.
2. Description of the Prior Art
The principle of a scroll fluid machine has been known for a long time and its application to various kinds of machine, such as compressors, pumps and expanders, has been thought of. Referring now to FIG. 1 which shows fundamental constituent elements of a scroll fluid machine, reference numeral 1 designates a fixed scroll, 2 designating an orbiting scroll, 1a designating a discharge port, P designating a compression chamber, O designating a fixed point of the fixed scroll 1, and O' designating a fixed point of the orbiting scroll 2. The fixed scroll 1 and the orbiting scroll 2 are provided with a pair of spiral side plates 101, 201, whose winding directions are opposite to each other and whose shapes are the same, being formed on bed plates (not shown) thereof, and being joined together as shown in FIG. 1, and said spiral side plates 101, 201 being brought into contact with each other on axial sides thereof at a plurality of points B at which said spiral side plate 101 is brought into contact with said spiral side plate 201. The spiral side plates 101, 201 have a shape of involute curve.
Next, the operation of the scroll fluid machine when operated as a compressor is described. Referring to FIG. 1, the fixed scroll 1 is stationary relatively to the space, the orbiting scroll 2 is stationary relatively to the space, the orbiting scroll 2 being joined with the fixed scroll 1 as shown in FIG. 1, and the orbiting scroll 2 carrying out a rotational motion without changing an attitude thereof relative to the space, in short carrying out a revolution without rotating on its own axis and with making a spiral center thereof eccentric to move by 0.degree., 90.degree., 180.degree. and 270.degree. as shown in FIG. 1. Said points B move toward the center with the movement of the orbiting scroll 2, a volume of the crescent-shaped compression chamber P defined by the spiral side plate 101 of the fixed scroll 1, the spiral side plate 201 of the orbiting scroll 2 and both spiral side plates 101, 201 being gradually reduced, and a gas introduced into the compression chamber P being compressed to be discharged through the discharge port 1a formed at the center in the radial direction of the fixed scroll 1. A distance from the point O to the point O' as shown in FIG. 1 is maintained constant during that period and provided that a thickness of both spiral side plates 101, 201 is t and a gap between both spiral side plates 101, 201 is z, O O'=z/2-t holds good.
In addition, if the orbiting scroll 2 is rotated in the opposite direction, in short by 0.degree., 270.degree., 180.degree. and 90.degree. as shown in FIG. 1, this scroll fluid machine operates as an expander.
The concrete construction of a scroll fluid machine operated on the basis of such an operation principle is described with reference to FIG. 2. Referring to FIG. 2, which is a sectional view showing the main parts of the conventional scroll fluid machine in the case where it is applied as a compression machine, reference numeral 1 designates a fixed scroll, 2 designating an orbiting scroll, 1a designating a discharge port, and P designating a compression chamber, similarly to FIG. 1. The fixed scroll 1 and the orbiting scroll 2 comprises a spiral side plate 101, 201 and a bed plate 102, 202, respectively. In addition, the orbiting scroll 2 is combined with the fixed scroll 1 under the condition that a surface opposite to a surface, where the spiral side plate 201 is formed, of the bed plate 202 is supported by a frame 4 as shown in FIG. 1 while the fixed scroll 1 is fixedly mounted on the frame 4. Further, A in the figure designates an axial gap between end faces 101a, 201a of the spiral side plates 101, 201 and bottom faces 202a, 102a of the bed plates 202, 102 facing to the spiral side plates 101, 201, respectively.
And, when a main shaft 3 connected to the orbiting scroll 2 is rotated as shown by an arrow, the orbiting scroll 2 carries out only a revolution without rotating on its own axis by means of an auto-rotation preventing device (not shown). As a result, a fluid to be compressed is sucked in through a suction port 1b formed on an outside end portion of the fixed scroll 1, compressed on the basis of the operation principle shown in FIG. 1, and exhausted through the discharge port 1a.
In such a fluid machine, since a fluid flowing in the radial direction of spiral through said gap A shows a leakage-line length corresponding to a peripheral length of spiral, it is relatively large compared to a volume of a fluid to be sucked in and its influence upon an efficiency of the machine is great.
A means, in which the gap A is made minute, an oil being sucked in together with a fluid to be compressed through the suction port 1b, and an oil film being formed in the minute gap A to prevent the fluid to be compressed from leaking, has been proposed for such a method of sealing in the radial direction, as shown in Japanese Patent Application Laid-Open No. 46081/1980.
However, problems have occurred in that the formation of such minute gaps uniformly requires a high dimensional accuracy for parts, such as the fixed scroll 1, the orbiting scroll 2 and the frame 4, and parts matching to each other in size must be selected in the assembly of such parts. Besides, the vicinity of the discharge port 1a is heated to high temperatures by the compressed fluid during the operation and as a result, when a thermal expansion of the spiral side plates exceed the minute gap A, the sticking is produced as there is not relief space. Accordingly, the thermal expansion of the spiral side plates must be assumed to previously increase the minute gap A so much as that. However, is so, the gap A exceeds the optimum gap required for the formation of the effective oil film and as a result the leakage is increased, whereby losing the sealing effect in many cases.
On the other hand, also a method, in which the end faces 101a, 201a of the spiral side plates 101, 201 are provided with a groove formed along the longitudinal direction of spirals and sealing material is inserted in this groove to prevent the leakage in a contact-sealing manner differently from the above described method of preventing the leakage by the formation of the oil film, has been thought of. Such a sealing method is formerly disclosed in U.S. Pat., No. 801,182, 1905 and recently in Japanese Patent Application Laid-Open No. 117304/1976.
Next, the preventing method disclosed in Japanese Patent Application Laid-Open No. 117304/1976 is described as one example with reference to FIGS. 3-5. Referring to FIG. 3, which is a partial sectional view showing a vicinity of the gap A between the bottom face 102a of the bed plate of the fixed scroll 1 and the end face 201a of the spiral side plate of the orbiting scroll 2, the end face 201a of the spiral side plate 201 is provided with a groove 5 opening along the longitudinal direction of spirals and having a rectangular cross section formed therein, a sealing material 51 having the same shape as the groove 5 being inserted in the groove 5. Here, the groove 5 and the sealing material 51 are prescribed in size so that an upper surface 51a of the sealing material 51 may be brought into contact with the bottom face 102a of the bed plate, a side face 51c of the sealing material 51 may be brought into contact with a side face 5c of the groove 5, a gap 501 may be formed in the longitudinal direction of spirals between a side face 5b of the groove 5 and a side face 51b of the sealing material 51, and a gap 502 may be formed similarly in the longitudinal direction of spirals between a bottom face 5d of the groove 5 and a lower surface 51d of the sealing material 51. And, as a result, even when the gap A exists between the end face 201a of the spiral side plate 201 and the bottom face 102a of the bed plate, the sealing between a high-pressure side compression chamber P.sub.H and a low-pressure side compression chamber P.sub.L partitioned by the spiral side plate 201 is performed by making the fluid flow into the gaps 401, 502 from the high-pressure side compression chamber P.sub.H as shown by a full arrow so that a force may act in a manner as shown by an arrow F. In short, the upper face 51a and the side face 51c of the sealing material 51 is pressed against the bottom face 102a of the bed plate and the side face 5c of the groove 5, respectively, the sealing material 51 is closely adhered to the bottom face 102a of the bed plate and the side face 5c of the groove 5 to prevent the fluid from leaking.
In a sealing method of this type, although the leakage of the fluid in the radial direction of spirals through the gap A between the end face of the spiral side plate and the bottom face of the bed plate can be effectively prevented, a problem has occurred in that the leakage is apt to occur in the longitudinal direction of spirals through the gaps 501, 502 between the compression chambers P partitioned by the spiral side plates 101, 201 at the points B.
This leakage is described in FIGS. 4, 5, in which FIG. 4 is a partial sectional view as seen from the upper face, showing the vicinity of the points of contact B where the spiral side plate 101 is brought into contact with the spiral side plate 201, and FIG. 5 is a partially sectioned perspective view showing the vicinity of the points of contact B as shown in FIG. 4.
These figures show the state in which the fluid is leaked from the high-pressure side compression chamber P to the low-pressure side compression chamber P through the gaps 501, 502 as shown by a full arrow. As above described, the sealing method of this type can effectively perform the sealing in the radial direction but since the gaps 501, 502 must be formed between the groove 5 and the sealing material 51 as the means for effectively sealing in the radial direction, it is inevitable that the leakage is produced in the longitudinal direction of spirals and a compression efficiency, in short a performance, is reduced. In particular, there is the possibility that the fluctuation of the gaps 501, 502 in size due to the machining accuracy leads to an increase of the leakage through the gaps 501, 502 or an increase of the leakage in the radial direction due to a reduction of the sealing material 51 in followability itself. In addition, since the upper face 51a of the sealing material 51 slides by being pressed against the bottom face 102a of the bed plate by the action of the fluid, also the sliding loss and abrasion can not be disregarded.
Besides, in order to prevent such a leakage in the longitudinal direction of spirals, for example in Japanese Utility Model Application Laid-Open No. 180181/1982, a width size D of the sealing material 51 is substantially equalized to that D' of the groove 5, and a thickness size H of the sealing material 51 is larger than a depth size H' of the groove 5, as shown in FIG. 6. However, in this method, the sizes H and H' are difficult to control and if H-H'&lt;A, an axial gap is opened to produce the leakage in the radial direction of spirals while if H-H'&gt;A, the sealing material 51 is to be put between the fixed scroll 1 and the orbiting scroll 2, whereby the smooth rotation is hindered.
As described above, the conventional scroll fluid machine has a problem in the accuracy control such as the machining accuracy required for making an axial minute gap uniformly in a method of forming an oil film. In addition, the conventional scroll fluid machine has shown the contradictory problems in that if the gap is made small, the end face of the spiral side plate is brought into contact with the opposite bed plate due to a thermal expansion in the operation and the like to produce the sticking, whereby lowering the reliability while if the gap is made large in order to prevent the above described problem, the performance is remarkably reduced. Besides, in a contact-sealing method, in the case where the gap is formed between the sealing material and the groove to followablly close by a pressure of a fluid, the problem occurs in the reduction of the performance due to the leakage through said gap and the abrasion of the sealing material. Furthermore, the case, where the gap is not formed between the sealing material and the groove and the sealing is carried out by means of sealing materials, has a problem in that the strict accuracy control is required similarly to the oil-film forming type method.